a) Field of the Invention
The present invention relates to a transport apparatus, method and system suitable for production lines of semiconductor devices and liquid crystal display devices.
b) Description of the Related Art
Most of production lines for semiconductor devices and liquid crystal display devices adopt a job shop production style which manages as one unit an apparatus group constituted of processing apparatuses having the same function or a large apparatus group constituted of apparatus groups. A plurality of apparatuses in each apparatus group and annexed loaders and unloaders are housed in each partitioned small room called a bay.
FIG. 17A is a plan view showing a layout of a conventional transport apparatus 20 which forms production lines of semiconductor devices. A main transport path 200 extending in a lateral direction in FIG. 17A is set in a generally central portion of the transport apparatus. Subsidiary transport paths 201 branch from the main transport path 200 at a plurality of predetermined positions of the main transport path 200. The subsidiary transport paths 201 are disposed on both sides of the main transport path 200. When attention is paid to one subsidiary transport path 201, this path 201 is disposed only on one side of the main transport path 200. One subsidiary path 201 corresponds to one bay. The subsidiary transport path is also called an intra-bay transport path. The main transport path 200 and subsidiary transport paths 201 transport a workpiece such as a wafer cassette.
A stocker 202 is provided for each subsidiary transport path 201. The stocker 202 transports a workpiece between the main transport path 200 and corresponding subsidiary transport path 201 and also temporarily stocks a workpiece. In order to transport a workpiece from one bay to another bay, the workpiece is transferred from the stocker 202 at the transport originating bay via the main transport path 200 to the stocker 202 of the transport destination bay. Namely, if a workpiece is transported from one bay to another bay, the main transport path 200 is used. The main transport path 200 is therefore called an inter-bay transport path.
Predetermined processing apparatuses 203 are disposed around the subsidiary transport path 201. Each processing apparatus receives a workpiece under transport on the subsidiary transport path 201 and executes a predetermined process to thereafter return the workpiece to the subsidiary transport path 201.
FIG. 17B is a plan view showing another layout of a conventional transport apparatus. In this example shown in FIG. 17B, subsidiary transports paths 201 are disposed only on one side of a main transport path 200. The other structures are the same as those shown in FIG. 17A. The transport apparatus shown in FIG. 17A follows a both-side bay system, and the transport apparatus shown in FIG. 17B follows a one-side bay system.
In determining a transport destination of a workpiece in one bay, a processing apparatus group which executes the next process for the workpiece is determined and then the stocker of the bay housing the determined processing group is determined as the transport destination.
In the transport apparatus, there are a plurality of workpieces to be processed at different process sequences. In order to process a workpiece having different process sequences, each processing apparatus is required to perform a process sequence switching work. For example, in the case of an exposure system, a work such as exchanging a photomask is required to be performed. In order to reduce a loss in the process sequence switching work, it is preferable to schedule the process sequence so that workpieces can be processed continuously by the same process. To this end, a plurality of workpieces which can be processed by the same process are stocked in the stocker 202 so that the workpieces capable of being processed by the same process can be supplied continuously.
It is necessary to supply a collection of workpieces to be processed by the same process to a processing apparatus which performs a batch process of processing a plurality of workpieces at the same time. Also to this end, it is necessary for the stocker 202 to stock a plurality of workpieces capable of being processed by the same process. The stocker 202 therefore stocks a plurality of workpieces to be processed at different process sequences, a set of workpieces to be processed by the same process being stocked separately.
In the transport apparatus of the both-side bay system shown in FIG. 17A, an average distance between the stocker 202 and processing apparatuses 203 in the bay is short so that a transport time in the bay can be made short. Since the subsidiary transport paths 201 are disposed on both sides of the main transport path 200, a number of connection points between the main path 200 and subsidiary transport path 201 can be provided. It is therefore easy to stepwise increase the number of bays. However, since the number of bays increases, a total transport distance including inter-bay transport is likely to become long. Particularly, the number of transfers between the main transport path 200 and subsidiary transport path 201 is likely to increase.
In the transport apparatus of the one-side bay system shown in FIG. 17B, it is possible to shorten the total transport distance including inter-bay transport and to reduce the number of transfers between the main transport path 200 and subsidiary transport path 201. However, an average transport distance in each bay is long. It is difficult to provide a number of connection points between the main transport path 200 and subsidiary transport path 201, so that this one-side bay system is not suitable for stepwise increasing the number of bays.
Also in the transport apparatuses shown in FIGS. 17A and 17B, if the stocker 202 is full of workpieces or is defective, a workpiece processed at one bay cannot be transported to the stocker 202 of another bay where the next process is performed. In order to deal with such a case, a method has been incorporated in which a temporary stocker for temporarily stocking a workpiece is defined to transfer the workpiece unable to be transported, to a desired bay. With this method, however, the number of transports for temporary stock increases. In addition, the temporary stocker may become full of workpieces unable to be transported so that workpieces to be stocked essentially in this stocker cannot be stocked.
The main path 200 and subsidiary transport path 201 shown in FIGS. 17A and 17B can be realized, for example, by a ceiling transport apparatus of the type that containers move on a rail mounted on a ceiling or by an unmanned ground transport truck running on a rail mounted on the ground. With this structure, it becomes necessary to independently provide for each processing apparatus a space for temporarily stocking workpieces such as semiconductor devices and liquid crystal display devices and a space for a loader/unloader to transfer a workpiece between the transport path and processing apparatus.
As a workpiece becomes large, the stock facility and loader/unloader also become large. Therefore, the area of a necessary clean room becomes large. As the processing apparatus becomes large, the transport path becomes long so that the number of necessary containers or unmanned trucks constituting the transport path increases.
A workpiece processed by a processing apparatus at one bay is transported to the next processing apparatus at another bay via the subsidiary transport path, a stocker, the transport path, another stocker, and another subsidiary transport path. Therefore, each processing apparatus is required to independently manage a cleanness degree.